Monopulse radar systems are essential for managing space debris during satellite exploration missions due to its high precision, angular measurement capabilities, and ability to track multiple objects at once, ensuring the safety and integrity of space assets. In this paper, a compact mm-wave, end-fire, high gain monopulse antenna is presented that could be fabricated on a thin PCB laminate. The reported results show good performances, a -10-dB impedance bandwidth of 60.6 % (23–43 GHz) for the sum and difference ports, better than 24 dB isolation between the input ports, the difference radiation patterns better than -25 dB null-depth. The proposed monopulse radar system could be used in a wide range of practical applications in detecting and managing space debris in satellite exploration missions.